1. Field of the Invention
This invention relates to plastic bags made from plastic sheeting such as those that may be used for packaging pet foods, foodstuffs and other bulk products. More specifically, this invention relates to the use of these plastic bags in a unique seamless configuration and the process of manufacturing them. This invention also relates to the use of these plastic bags in a unique system which provides for filling and sealing the bags with bulk contents such as pet foods, foodstuffs, concrete, plaster, and the like, in an automated process with a substantially dust-free environment.
2. Description of the Related Art
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
Currently, most bags used for bulk contents are standard side-gusseted plastic bags, typically four to five mils thick and are filled from the top bag mouth, then sealed (or sewn closed) and palletized for shipping. Plastic bags of this variety are usually made from sheeting, as opposed to tubing and are highly desirable for bulk use such as packaging fertilizer, lawn maintenance products, seed bags, salt, kitty litter and so on. Generally speaking, these bags are put up in larger sizes to handle loads from as little as 5 pounds to as much as 100 pounds.
The primary reason that sheeting is used to form these bags is that they may be expertly printed in up to 6 colors with process-tone print quality on all panels—front, back and the two sides and, at times, the top and bottom. To make a prior art bag, the printed sheeting is folded over and formed into a layflat tube, the open side edges are matched flush atop one another in the machine direction, lap-sealed (a continuous heat seal), gusseted on the sides, then cut and sealed along a bottom edge to form a bag. This type of high quality printing is restricted on tube-type bags since they are printed independently on the front and the back panels while in a two-sided layflat configuration, before being gusseted. Thus, print registration from front to back is extremely difficult to hold. In the outer portion of the layflat surfaces that become the front and rear gusset panels of the side gussets, it is commonly understood that print copy on the front panel of a gusset should not be attempted to be registered with print copy on the back panel of a side gusset. A further problem with printing tube stock is that the number of colors available to each independent surface is reduced. Since most printing presses have a maximum of 6 print stations (6 colors), there are only 6 color stations total that must be divided between the two surfaces, front and back. Thus, it is impossible to print 6-color process tone print quality on two sides, which would require a total of 12 stations: a set of 6 stations for each independent front and back surface.
When manufacturing a prior art lap seal bag, the two open edges are matched and externally sealed with about a ¼″ “lap seal”, sealing the two matched edges together, thus forming a tube. When later gusseting the bag, this lap seal seam is usually registered on an outer gusset edge since it naturally points outward anyway. After gusseting, the bag is formed by heat sealing the bottom edge and cutting the top-open bag mouth. This is a fairly common manufacturing process used in industry today. The ¼″ lap seal seam that protrudes outward at the gusset edge may distort or interrupt the printing on the bag. Generally speaking, it is undesirable to print where a bag is going to be lap (heat) sealed, as the ink tends to build up on the lap sealer's heat elements when sealing along the printed film edges. But it is also undesirable to leave a lap seal strip unprinted and disrupt the continuity of attractive graphics. Thus, this becomes a predicament to the graphic artist, the bag manufacturer and the retailer.
Most bags used with cement and concrete products and other heavy flowable contents are large multiwall paper bags with fill valves, like those commonly seen palletized in home improvement centers throughout the U.S. They typically contain products, such as 60# mortar and concrete mix and 94# cement and concrete mix, sold to consumers for use in home garden and yard applications. The chief reason paper valve bags are used for these applications is primarily due to per unit cost and productivity factors. Paper valve bags cost more than standard, top-loading plastic bags, but the paper bags are much faster to fill, thus substantially improving productivity and output. There has been some limited use of plastic valve bags made from a woven polypropylene—specially in Europe—that do not lower productivity. But in the U.S. and other countries where paper is still relatively inexpensive, the polypropylene valve bags cost quite a bit more. One of the main reasons they cost more than traditional polyethylene top loading bags is because the equipment used to manufacture them is extremely expensive—as much as ten times that of a standard plastic bag machine.
As anyone experienced in the art knows, there are several problems associated with the prior art. In addition to the high cost, other disadvantages of paper packaging include the consumption of five times the storage space of plastic; the vulnerability of cement and concrete products stored in paper to weather conditions (especially rain), and the vulnerability of paper to pest infestations. In contrast, the superior environmental qualities of plastic are becoming commonly known to retailers and users throughout the country and would be desirable, if practical.
Without question, if a plastic bag could be developed that could eliminate the external lap-sealed seam from sticking out and interrupting print graphics, it would be highly desirable in many applications. Moreover, if a plastic valve bag and system could be developed that could replace the multiwall paper bags cost effectively, without reducing productivity, it would be highly desirable. In fact, if a plastic valve bag were developed that could compete favorably with standard top-fill plastic bags, that too would be highly desirable.